Ch. XXX.] 



THE POST-PLIOCENE PERIOD. 



Fig. 662. 



525 



C]ay. 

 b. 



Lava. 



Clay. 

 b. 



Altered. Lava. Clay, &c. 

 c. a. h. 



Post-Pliocene strata invaded by lava, I.^le of Cyclops (laorizontal section). 

 a. Lava. b. Laminated clay and sand. c. The same altered. 



of Campania is known to have undergone during the last 2000 years. 

 The aggregate effect of igneous operations during that period is far 

 from insignificant^ comprising as it does the formation of the modern 

 cone of Vesuvius since the year 79, and the production of several minor 

 cones in Ischia, together with that of Monte Nuovo in the year 1538. 

 Lava-currents have also flowed upon the land and along the bottom of 

 the sea — volcanic sand, pumice, and scoria? have been showered down 

 so abundantly, that whole cities were buried — tracts of the sea have 

 been filled up or converted into shoals — and tufaceous sediment has 

 been transported by rivers and land-floods to the sea. There are also 

 proofs, during the same recent period, of a permanent alteration of the 

 relative levels of the land and sea in several places, and of the same 

 tract having, near Puzzuoli, been alternately upheaved and depressed to 

 the amount of more than 20 feet. In connection with these convul- 

 sions, there are found, on the shores of the Bay of Baiae, recent tufa- 

 ceous strata, filled with articles fabricated by the hands of man, and 

 mingled with marine shells. 



It was also stated in this work (p. 119), that when we examine this 

 same region, it is found to consist largely of tufaceous strata, of a date 

 anterior to human history or tradition, which are of such thickness as 

 to constitute hills from 500 to more than 2000 feet in height. These 

 post-pliocene strata, contaiDing recent marine shells, alternate with dis- 

 tinct currents and sheets of lava v\^hich were of contemporaneous origin ; 

 and we find that in Vesuvius itself, the ancient cone called Somma is of 

 far greater volume than the modern cone, and is intersected by a far 

 greater number of dikes. In contrasting this ancient part of the moun- 

 tain with that of modern date, one principal point of difference is ob- 

 served ; namely, the greater frequency in the older cone of fragments 



